Flexible ofdm/ofdma frame structure for communication systems

ABSTRACT

A flexible OFDM/OFDMA frame structure technology for communication systems is disclosed. The OFDM frame structure technology comprises a configurable-length frame which contains a variable length subframe structure to effectively utilize OFDM bandwidth. Furthermore, the frame structure facilitates spectrum sharing between multiple communication systems.

RELATED PATENT APPLICATIONS

This application claims benefit of priority under 35 U.S.C. § 119(e) toProvisional Application No. 60/986,809, entitled “Flexible OFDM/OFDMAFrame Structure For Communication Systems”, filed Nov. 9, 2007;Provisional Application No. 60/987,747, entitled “Flexible OFDM/OFDMAFrame Structure For Communication Systems”, filed Nov. 13, 2007;Provisional Application No. 61/020,690, entitled “Flexible OFDM/OFDMAFrame Structure For Communication Systems”, filed Jan. 11, 2008;Provisional Application No. 61/021,442, entitled “Flexible OFDM/OFDMAFrame Structure For Communication Systems”, filed Jan. 16, 2008;Provisional Application No. 61/031,658, entitled “Flexible OFDM/OFDMAFrame Structure For Communication Systems”, filed Feb. 26, 2008; andProvisional Application No. 61/038,030, entitled “OFDM/OFDMA FrameStructure For Communication Systems”, filed Mar. 19, 2008, all of whichare incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to digital communications andmore particularly to Orthogonal Frequency Division Multiplexing (OFDM)or Orthogonal Frequency Division Multiple Access (OFDMA) systems.

BACKGROUND OF THE INVENTION

There is an increasing need for mobile high-speed communication systemsto provide a variety of services such as downloading music files, TV,Internet, and photo sharing. A mobile high-speed communication systemmust overcome many difficult operating conditions. Among the manyconditions the system must contend with are interference, multipathsignals, changing obstructions to the signal line-of-site, Dopplershift, inter-symbol interference (ISI), and changing distances betweentransmitter and receiver. Orthogonal Frequency Division Multiplexing(OFDM) is one technique developed for high-speed communications that canmitigate many of these difficult conditions.

OFDM divides an allocated communication channel into a number oforthogonal subchannels of equal bandwidth. Each subchannel is modulatedby a unique group of subcarrier signals, whose frequencies are equallyand minimally spaced for optimal bandwidth efficiency. The group ofsubcarrier signals are chosen to be orthogonal, meaning the innerproduct of any two of the subcarriers equals zero. An inverse fastFourier transform (IFFT) is often used to form the subcarriers. Thenumber of orthogonal subcarriers determines the fast Fourier transform(FFT) size (N) to be used.

Orthogonal Frequency Division Multiple Access (OFDMA) is a multi-userversion of OFDM. For a communication device such as a base station (BS),multiple access is accomplished by assigning subsets of the orthogonalsub-carriers to individual subscriber devices, such as mobile stations(MS), with which the base station is communicating. OFDMA may beconsidered to be a combination of frequency and time domain multipleaccess, where a time-frequency space is partitioned and the mobilestation data is assigned along the OFDM symbols and subcarriers.

In telecommunications, a frame is a fixed or variable length packet ofdata, encoded in accordance with a communication protocol for digitaltransmission. A frame structure defines the way a multiplexer divides acommunication channel into frames for transmission. The frame structureof an OFDM or OFDMA system has a major impact on the performance of thesystem. Currently, there is limited choice for high performance OFDM andOFDMA frame structures. Therefore, there is a need for systems andmethods that provide a flexible frame structure for high performanceOFDM and OFDMA systems.

In particular, the 802.16e amendment to the IEEE 802.16 standard, whichis referred to as “802.16e” or simply as “16e” herein, has defined arelatively rigid frame structure in accordance with theWirelessMAN-OFDMA Reference System. A new amendment to the IEEE 802.16standard, the 802.16m amendment, which is referred to as “802.16m” orsimply as “16m” herein, has been proposed. Requirements for thedevelopment of the 802.16m as specified by IEEE 802.16m SystemRequirements Document (IEEE 802.16m SRD), IEEE 802.16m-07/002r4, Oct.19, 2007, which is incorporated by reference herein in its entirety,stipulate many improvements in performance over the 802.16eWirelessMAN-OFDMA Reference System and operation in many differentdeployment environments. Improvements in performance include reductionsin latency across the air interface, increases in user and sectorthroughput, and reductions in system overhead. Operation is alsorequired in the presence of varying levels of mobility, from stationaryup to 350 km/h and beyond, and in sectors and cells with drasticallydifferent coverage ranges, from micro-cells and even femto-cells withcoverage ranges in the 10's to 100's meters to large rural macro-cellswith coverage ranges greater than 5 kilometers.

The relatively rigid frame structure that currently exists in IEEE802.16e operating with the OFDMA physical layer is unlikely to maximizethe achievable performance under such diverse deployments andoperational conditions. Therefore, there is a need for a more flexibleframe structure that allows maximal performance to be more readilyachieved under the given deployment and operational conditions.

An added constraint on the system design of IEEE 802.16m is therequirement to support legacy Mobile Stations (MS) that conform to IEEE802.16e WirelessMAN-OFDMA Reference System on the same radio frequencycarrier simultaneously with IEEE 802.16m MSs. In this mixed mode ofoperation, the legacy MSs must be able to operate as if they were beingserved by a Base Station (BS) that conforms only to theWirelessMAN-OFDMA Reference System. Therefore, there is also a need foran IEEE 802.16m frame structure that provides support for legacy MSsunder IEEE 802.16e.

SUMMARY OF THE INVENTION

A flexible OFDM/OFDMA frame structure for communication systems isdisclosed. The OFDM frame structure comprises a configurable-lengthframe which contains a variable length subframe structure to effectivelyutilize OFDM bandwidth. Furthermore, the frame structure facilitatesspectrum sharing between multiple wireless communication systems.

In one embodiment of the invention, the OFDM/OFDMA frame structure iscomprised of a time series of successive fixed length frames with eachframe subdivided into one or more variable length subframes and witheach subframe being an integer number of a unit subframe in duration.While the durations of the frames, T_(frame), and unit subframes,T_(u-sub), are fixed for a particular instantiation of the OFDM/OFDMAframe structure, they may take on different values for differentinstantiations of the OFDM/OFDMA frame structure. Example framedurations may be T_(frame)=5, 10, and 20 ms. Example unit subframedurations may be T_(u-sub)=0.5, 0.675, 1, 1.25, 1.5, and 2 ms. Thisflexibility in configuration of frame durations and unit subframedurations facilitate the co-existence of current and future systemsbased on current and future industry standards such as Third GenerationPartnership Project Long Term Evolution (3GPP LTE), Third GenerationPartnership Project 2 Ultra Mobile Broadband (3GPP2 UMB), TimeDivision-Synchronous Code Division Multiple Access (TD-SCDMA), WirelessInteroperability for Microwave Access (WiMAX), and the like.

In another embodiment of the invention, the start of an OFDM/OFDMA frameis identifiable by the presence of a Frame Sync and Control signal thatis transmitted on the downlink at the start of the first subframe of theframe. The Frame Sync and Control signal possesses properties thatdistinguish this start of frame transmission from similar transmissions,such as transmissions from other sources within this OFDM/OFDMA systemor from systems of other Time Division Multiplexed (TDM) basedtransmission technologies that are sharing the same transmission medium(e.g., same radio frequencies), such as Wireless Interoperability forMicrowave Access (WiMAX).

In another embodiment of the invention, the Frame Sync and Controlsignal that is located at the start of the OFDM/OFDMA frame containscontrol information that a compatible device can receive and decode todetermine the subframe structure within the frame. This frame controlinformation flexibly supports specification of subframes with durationsand directions (i.e., downlink or uplink) that can vary within a frameand also from frame to frame. This flexibility allows the OFDM/OFDMAframe structure to be adapted to accommodate dynamic Quality of Service(QoS) and system control requirements of the data being carried acrossthe OFDM/OFDMA air interface.

In another embodiment of the invention, one or more subframes within aframe can be set aside for use by transmissions from other sources, suchas other sources within the same OFDM/OFDMA system, or from systems ofother Time Division Multiplexed (TDM) based transmission technologiesthat are sharing the same transmission medium (e.g., same radiofrequencies), such as Wireless Interoperability for Microwave Access(WiMAX). The flexibility in the configuration of the frame and unitsubframe durations, and of the dynamic subframe durations within framesallows the TDM timing and framing requirements of other technologies tobe easily accommodated.

In another embodiment of the invention, areas of the time-frequencyphysical transmission resource space in one or more subframes within aframe can be set aside for use by transmissions from other sources, suchas other sources within the same OFDM/OFDMA system, or from systems ofother Time Division Multiplexed (TDM) based transmission technologiesthat are sharing the same transmission medium (e.g., same radiofrequencies), such as Wireless Interoperability for Microwave Access(WiMAX). This approach is advantageous when the other transmissionsources occupy only a subset of the transmission frequencies of theprimary source (i.e., the transmitter of the Frame Sync and Controlsignal for this OFDM/OFDMA frame structure).

In yet another embodiment of the invention, a method is described fordefining an IEEE 802.16m proposed standard (16m) frame structure withlegacy support for IEEE 802.16e standard (16e) frame requirements. Themethod adds flexibility to allow frame partitioning and timing to fitlegacy 16e frame requirements. The method may start with a frame designtailored to meet 16m requirements (e.g., shorter delay, lower controloverhead, etc.), and then fit legacy 16e frames and subframes into the16m frame structure by appropriate resource reservation.

In another embodiment of the invention, the frame is further dividedinto Frame Partitions where each Frame Partition contains local controlinformation for the partition located at some known location within thepartition, and where the location of the start of the partition ispointed to by the control information in the previous partition. Thelocal control information within the Frame Partition contains framecontrol information applicable to the partition, which at a minimumincludes the location, size and direction of subframes within thepartition, and may include the location and size of data transmissionallocations within the subframes as well as other types of broadcastcontrol information for the partition.

In another embodiment of the invention, control information in a primarycarrier provides control of transmissions and resource allocations in asecondary carrier. This secondary carrier may or may not be adjacent tothe primary carrier, and the resources of one or more of these secondarycarriers together with the resources of the primary carrier constitutethe available resources for the Base Station (BS).

In another embodiment of the invention, all subframes of the primarycarrier are for the downlink direction (from BS to MS) and all subframesof a secondary carrier are for the uplink direction (from MS to BS),which represents a special case of the frame structure configurationdescribed herein that can be applied to a Frequency Division Duplex(FDD) arrangement of carriers belonging to a BS.

In another embodiment of the invention, the physical layer of anOFDM/OFDMA communication system is based on a fixed subcarrier spacingof 12.5 kHz. The 12.5 kHz subcarrier spacing is applied for all thechannel bandwidth, e.g., 5/10/20 MHz, 3.5/7/14 MHz and also 8.75 MHz.The 12.5 kHz subcarrier spacing serves well in all the radioenvironments that 802.16m is intended to operate in, and is highlycompatible with available and potential future carrier bandwidths.

In another embodiment of the invention, three cyclic prefix (CP) lengthsbased on the 12.5 kHz subcarrier spacing are provided and used fordifferent radio scenarios. These three CP lengths are needed toadequately balance the required length of CP with the loss of capacitydue to the CP in order to serve the breadth of radio environmentsenvisaged for 802.16m. The three CP lengths are 2.5 us, 10 us, and 15us.

Further features and advantages of the present invention, as well as thestructure and operation of various embodiments of the present invention,are described in detail below with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, in accordance with one or more variousembodiments, is described in detail with reference to the followingFigures. The drawings are provided for purposes of illustration only andmerely depict exemplary embodiments of the invention. These drawings areprovided to facilitate the reader's understanding of the invention andshould not be considered limiting of the breadth, scope, orapplicability of the invention. It should be noted that for clarity andease of illustration these drawings are not necessarily made to scale.

FIG. 1 illustrates a general TDD frame structure according to oneembodiment of the invention.

FIG. 2 illustrates an exemplary method of frame control according to oneembodiment of the invention.

FIG. 3 illustrates another exemplary method of frame control accordingto one embodiment of the invention.

FIG. 4 illustrates an exemplary method of spectrum sharing with otherTDM-based transmission technologies according to one embodiment of theinvention.

FIG. 5 illustrates another exemplary method of spectrum sharing withother TDM-based transmission technologies according to one embodiment ofthe invention.

FIG. 6 illustrates another aspect of the exemplary method of spectrumsharing in FIG. 5 according to one embodiment of the invention.

FIG. 7 illustrates an exemplary method of frame control of a secondarycarrier from a primary carrier according to one embodiment of theinvention.

FIG. 8 illustrates how the exemplary method of secondary-carrier controlas shown in FIG. 7 can be applied to an FDD mode of operation accordingto one embodiment of the invention.

FIG. 9 illustrates an 802.16m Time Division Duplex frame structure withlegacy 802.16e support according to one embodiment of the invention.

FIG. 10 illustrates the basic format and major elements of a proposed802.16m frame according to one embodiment of the invention.

FIG. 11 illustrates some examples of unit subframe formats that can beapplied to DL subframe partitions according to one embodiment of theinvention.

FIG. 12 illustrates an exemplary method of legacy 802.16e frame supportvia TDM according to one embodiment of the invention.

FIG. 13 illustrates an FDD frame structure according to one embodimentof the invention.

FIG. 14 illustrates an exemplary operation of adjacent carrier andoverlay carrier deployments with legacy subcarrier spacing.

FIG. 15 illustrates an exemplary operation of multi-carrier deploymentwith guard bands.

FIG. 16 illustrates an exemplary operation of mixed system bandwidthsmulti-carrier deployment.

FIG. 17 illustrates an exemplary operation of mixed bandwidthsmulti-Carrier deployment without guard bands.

FIG. 18 illustrates an exemplary operation of carrier mis-alignment dueto different rasters.

FIG. 19 illustrates an 802.16m system having 12.5-kHz subcarrier spacingaccording to one embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following description of exemplary embodiments, reference is madeto the accompanying drawings which form a part hereof, and in which itis shown by way of illustration of specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the preferred embodiments of the invention.

The present invention is directed toward systems and methods forOFDM/OFDMA frame structure technology for communication systems.Embodiments of the invention are described herein in the context of onepractical application, namely, communication between a base station anda plurality of mobile devices. In this context, the example system isapplicable to provide data communications between the base station andthe plurality of mobile devices.

The invention, however, is not limited to such base station and mobiledevice communications applications, and the methods described herein mayalso be utilized in other applications such as mobile-to-mobilecommunications, wireless local loop communications, wireless relaycommunications, or wireless backhaul communications, for example.

In order to provide the most flexibility to meet the requirement ofcurrent and future systems, the basic frame definition in accordancewith embodiments of the present invention may include five elements inhierarchical order: frame; frame partition; subframe; subframepartition; and unit subframe. Each of these five frame elements will bedescribed below.

A frame provides the main outer structure that governs how quickly MSscan acquire synchronization with the frame boundaries and begincommunications with a BS. Therefore, a frame is primarily characterizedby a length, the presence of a synchronization signal, which istypically a Preamble at the beginning of the frame, and controlinformation that pertains to the frame.

The frame length is therefore set as a tradeoff between how quickly MSscan acquire or re-acquire synchronization and how often the overhead ofthe frame synchronization and control information is incurred.Considerations for synchronization delay include time to begin orre-acquire communications with a BS, such as on initial network entry oron recovery after synchronization loss, or time to perform rudimentarysignal measurements on the BS, such as during neighbor scanning tosupport handover.

A frame partition is a sub-slice of the frame that provides a shortertimeframe for scheduling relevance. This means that decisions on radioresource structures and assignments for a frame partition are made atthe beginning of the frame partition and generally cannot be altered.These are communicated to MSs via the Frame Partition Control signalingthat appears at the beginning of the frame partition.

A frame partition is comprised of one or more subframes, where the firstsubframe must be a DL subframe in order to accommodate the FramePartition Control signaling.

The length of a frame partition is generally dynamically set on a framepartition by frame partition basis based on the available queued DLtraffic and outstanding UL data requests and the available DL and ULradio resources in the next subframes in the frame, although if theavailable locations within a frame where a frame partition may begin arebased on fixed locations where frame partition control signaling may belocated, the available lengths of frame partitions may also beconstrained accordingly. In this way, the scheduling horizon and thefrequency of Frame Partition Control signaling adapts with the trafficload (i.e., becomes longer and less frequent as the traffic loadincreases). The maximum length of a frame partition is governed by themaximum tolerable delay for emergency signaling and may become relevantif the maximum length is shorter than the length of a frame. There areone or more frame partitions in a frame.

A subframe is defined as a contiguous number of time units of radioresources within a frame that has the same direction property—i.e.,either downlink or uplink. Therefore, a subframe is characterized by twoparameters: 1) a direction (downlink or uplink) and 2) a length orduration. This definition essentially retains the definition of subframefrom the WirelessMAN-OFDMA Reference System except that there may be twoconsecutive subframes that possess the same directionality (e.g.downlink subframe followed by another downlink subframe) if thesubframes belong to different frame partitions.

The granularity with which the length of subframes can be set isgoverned by the unit subframe since a subframe contains an integernumber of unit subframes, with the minimum length being 1 unit subframeand the maximum length being governed by the length of the framepartition in which the subframe belongs.

Since the length of subframes govern the rate of change of linkdirection in TDD operation, the subframe configuration has a directimpact on air interface transfer latency and therefore, on QoS and onsignaling response latency.

A subframe is comprised of one or more subframe partitions. Differentsubframe partitions may operate with different physical layer settingsthat may be better suited for communications with a certain set of MSs.This is analogous to the concept of permutation zone of theWirelessMAN-OFDMA Reference System, but with an important distinctionsince there may be other parameters that can be set differently betweensubframe partitions than subcarrier permutations. A subframe partitionis comprised of one or more unit subframes of identical or compatibleconfigurations, and therefore, is an integer number of unit subframes inlength.

The number and lengths of subframe partitions are set on a subframe bysubframe basis based on what may be the best configuration for the MSsand traffic being serviced at a particular time. A subframe partition ischaracterized by a length and properties of its constituent unitsubframe(s).

The radio resource allocation for a specific burst transmission may becomprised of a set of one or more individually addressable radioresource allocable units from within the unit subframes of a subframepartition. Burst transmissions do not occur across subframe partitionboundaries.

A unit subframe is defined as a continuous time interval of radioresources across the entire bandwidth (i.e., all subcarriers) of a radiocarrier that possesses a particular physical-layer structure, such aspilot and data subcarrier organization, radio resource allocationstructure, OFDM symbol structure, and idle time length and location.Units of radio resource allocations by the Medium Access Control (MAC)are defined within the boundaries of a unit subframe and therefore, aunit subframe also represents the largest individually addressable radioresource allocable unit. A unit subframe may be subdivided into smallerunits of radio resources that are individually addressable, butindividually addressable radio resource allocable units do not crossunit subframe boundaries. Alternatively, radio resource allocable unitsand therefore, correspondingly the address space for radio resourceallocations may be defined within the span of a subframe partition.

The nature of the physical layer parameter settings that may be set on aunit-subframe basis is a topic for further study and will be governed bythe possible physical layer radio resource configurations to be defined.A unit subframe is comprised of one or more (typically several)contiguous OFDM symbol periods and one or more idle times across allsubcarriers of radio carrier.

The unit subframe is the smallest time-unit building block of the framestructure.

A frame structure that includes all the five elements described aboveprovides the most flexibility to meet the requirement of current andfuture systems. However, in alternative embodiments, one or more frameelements might be eliminated to reduce frame control overhead and toimprove the performance of a particular system.

FIG. 1 is an illustration of an exemplary OFDM/OFDMA frame operating inTime Division Duplex (TDD) mode in accordance with one embodiment of theinvention.

The OFDM/OFDMA TDD frame definition 100 includes: a frame duration(T_(frame)) 100, a Frame Sync and Control signal 102, one or moredownlink subframes 103 and 104 of varying durations, and one or moreuplink subframes 105 and 106 of varying durations. A subframe comprisesan integer number of unit subframe durations (T_(u-sub)) 101. Adjacentsubframes may provide communications in the same direction, such as 105and 103/104, or may provide communications in opposite directions, suchas 103/106. The first subframe 108 is a downlink subframe and containsthe Frame Sync and Control signal 102.

The frame sync signal within the Frame Sync and Control signal 102 isgenerally a signal with unique known properties that allow it to beeasily distinguishable from other signals in the frame and from framesync signals of other transmission sources that may be using the sametransmission medium (e.g., the same radio frequencies). Equivalently,the frame sync signal exhibits strong autocorrelation properties (thatis, values of its autocorrelation function have a distinctive peak whenthe signal is compared to an aligned copy of itself) and weakcross-correlation properties with other signals in the frame or withother frame sync signals of other transmission sources that may be usingthe same transmission medium. Besides its property of uniqueness, theframe sync signal commonly also possesses other useful properties thatassist the receiver to properly demodulate and decode the other controland data signals within the frame. Being located at the start of theframe, the frame sync signal in the Frame Sync and Control signal shownin FIG. 1 is generally known as a Preamble of the frame.

FIG. 2 is an illustration of an exemplary method of control of thesubframe structure of a frame according to an embodiment of theinvention. In this method, the Frame Sync and Control signal 200 definesthe subframe structure of the entire frame. This subframe structuredefinition includes at least the following control information: 1)pointers 201 to the time location of the start of each subframe withinthe frame, 2) the directionality 202 of each subframe (i.e., whether thesubframe is used for downlink or uplink transmissions), and 3) the timeduration T_(sub) 203 of each subframe.

The subframe pointers 201 may be implemented in a number of ways. Oneimplementation is as a time offset from a known time reference point,such as from the start of the frame. There are also several options forthe time unit in which the subframe time offset is expressed, such as interms of a clock-based time unit (e.g., microseconds or milliseconds) orin terms of the duration (T_(u-sub)) of the unit subframe. Since eachsubframe is defined to be an integer number of unit subframes,expressing the duration of a subframe in terms of the number of unitsubframes is the most efficient since this results in the minimum numberof information bits needed to express the subframe duration. Therefore,the time offset to the start of each subframe in the frame can beexpressed as an integer number of unit subframes from the start of theframe.

As a refinement to this method, a more optimal way to define the startof each subframe is to combine it with the specification of thedurations of subframes by arranging the durations as a vector in whichthe subframe durations are listed in their order from the start of theframe. With this refined method, the time offset from the start of theframe to the start of a subframe within the frame is the sum of thedurations of all of the intervening subframes from the start of theframe to that subframe. With reference to the vector organization of thedurations of the subframes within a frame, the time offset to the n^(th)subframe may be expressed as:

${T_{{offset} - {sub}}\lbrack n\rbrack} = {\sum\limits_{i = 1}^{n - 1}{{T_{sub}\lbrack i\rbrack}.}}$

The subframe directionality 202 can take on one of two values (i.e.,downlink or uplink) and thus, can be represented by 1 bit of controlinformation per subframe. This subframe direction control bit may begrouped together with the other attributes of each subframe or may beorganized as a vector of subframe direction control bits indexed in theorder of subframe starting from the 1^(st) subframe at the beginning ofthe frame. These are examples of ways of organizing the subframedirection control information within a frame; other ways are possible.In order to reduce control signaling overhead at the expense of framestructure flexibility, the applicable frame structure may be selectablefrom a set of predefined settings in which the positions, lengths anddirectionalities of subframes within a frame would not need to beindividually signaled.

FIG. 3 is an illustration of another exemplary method of control of thesubframe structure of a frame according to an embodiment of theinvention. In this method, consecutive subframes within a frame aregrouped into Frame Partitions 310. A frame may be comprised of a one ormore Frame Partitions and the Frame Partitions may be of differentdurations. A Frame Partition provides more localized control of subframestructure within a frame. Another benefit of Frame Partitions is theflexibility to shorten the scheduling window to timeframes that areshorter than the duration of a frame, which can benefit the schedulingof time-critical traffic.

A Frame Partition 310 is comprised firstly of a downlink subframe whichcontains a Frame Partition Control data block 311 that is situated at aknown location in the subframe (for example, located at the upper leftcorner of the frequency-time space of this first downlink subframewithin a Frame Partition as shown in FIG. 3). Following the firstdownlink subframe, there may be 0 or more other subframes of varyingdurations and various directionalities that comprise the FramePartition. The maximum duration of any Frame Partition is constrained bythe number of unit subframe times remaining from the start of the FramePartition to the end of the frame.

The Frame Partition Control 311 defines the subframe structure of theFrame Partition. This subframe structure definition includes at leastthe following control information: 1) pointers 313 to the time locationof the start of each subframe that follows the first downlink subframewithin the Frame Partition, 2) the directionality 314 of each subframe(i.e., whether the subframe is used for downlink or uplinktransmissions) that follows the first downlink subframe within the FramePartition, 3) the time duration T_(sub) 315 of each subframe, and 4) apointer 312 to the start of the next Frame Partition in the frame. Ifthe structure of a frame is selected from a predefined set, thelocations, durations and directionalities of the subframes within theframe partition are implicit by the location of the start of the framepartition within the frame, and therefore, would not need to beexplicitly signaled.

The subframe pointers 313 may be implemented in a number of ways. Oneimplementation is as a time offset from a known time reference point,such as from the start of the Frame Partition. There are also severaloptions for the time unit in which the subframe time offset isexpressed, such as in terms of a clock-based time unit (e.g.,microseconds or milliseconds) or in terms of the duration (T_(u-sub)) ofthe unit subframe. Since each subframe is defined to be an integernumber of unit subframes, expressing the duration of a subframe in termsof the number of unit subframes is the most efficient since this resultsin the minimum number of information bits needed to express the subframeduration. Therefore, the time offset to the start of each subframe inthe Frame Partition can be expressed as an integer number of unitsubframes from the start of the Frame Partition.

As a refinement to this method, a more optimal way to define the startof each subframe is to combine it with the specification of thedurations of subframes by arranging the durations as a vector in whichthe subframe durations are listed in their order from the start of theFrame Partition. With this refined method, the time offset from thestart of the Frame Partition to the start of a subframe within the FramePartition is the sum of the durations of all of the interveningsubframes from the start of the Frame Partition to that subframe. Withreference to the vector organization of the durations of the subframeswithin a Frame Partition, the time offset to the n^(th) subframe may beexpressed as:

${T_{{offset} - {sub}}\lbrack n\rbrack} = {\sum\limits_{i = 1}^{n - 1}{{T_{sub}\lbrack i\rbrack}.}}$

The subframe directionality 314 can take on one of two values (i.e.,downlink or uplink) and thus, can be represented by 1 bit of controlinformation per subframe. This subframe direction control bit may begrouped together with the other attributes of each subframe or may beorganized as a vector of subframe direction control bits indexed in theorder of subframe starting from the 1^(st) subframe at the beginning ofthe Frame Partition. These are examples of ways of organizing thesubframe direction control information within a Frame Partition; otherways are possible.

The pointers 312 that are located in the Frame Partition Controlinformation in each Frame Partition and that specifies the time locationof the start of the next Frame Partition may be implemented in a numberof ways. One implementation is as a time offset from a known timereference point, such as from the start of the Frame Partition. If thetime unit used to specify this time offset is in terms of the duration(T_(u-sub)) of the unit subframe, the time offset to the start of thenext Frame Partition can be expressed as an integer number of unitsubframes from the start of this Frame Partition. For the last FramePartition in the frame, the pointer 312 contains a suitable unique valueto indicate that there is no further next Frame Partition within theframe.

In the method of FIG. 3, the frame control information contained in theFrame Sync and Control signal 300 includes information that applies toan entire frame basis. Such information may include the duration of theframe, the number of Frame Partitions in the frame, the unit subframeduration T_(u-sub), any restrictions on which subcarriers in theOFDM/OFDMA signal is valid within the frame, and so on.

FIG. 4 is an illustration of an exemplary method for the support ofspectrum sharing with another system based on otherTime-Division-Multiplexed (TDM) based transmission technologiesaccording to an embodiment of the invention. With the flexibilityallowed in the settings of the unit subframe duration T_(u-sub) 401 andthe frame duration 400, spectrum sharing in a time division multiplexedfashion can be easily accommodated supporting the other technology'srequirements in terms of frame and subframe timing as applicable. Theonly requirement on the other technology is that it not require full useof its operating spectrum at all times.

In this spectrum sharing method, certain subframe durations 404 within aframe may be reserved for the other system's use. Those subframedurations are managed within the current system such that there are notransmissions, downlink or uplink, by the current system during thosetimes. This means that these reserved subframe durations require specialdesignation within the current system. There are many ways in which thisdesignation can be accomplished. One exemplary method of designatingthese reserved subframe durations is to define them in the normal mannerin which subframes of the current system are defined, such as accordingto methods described above, and to enhance the definition of thesubframe directionalities as described above to include a new statevalue that indicates directionality does not apply to this subframe andthereby indicating that the particular subframe time is not used by thecurrent system.

The subframe durations 404 reserved for other-system use follow the samepolicies as durations of subframes active within the current system.Specifically, these durations are defined as integer multiples of theunit subframe duration 401.

There is no restriction that the physical parameters of thetransmissions in the subframes of the current system and in thesubframes durations reserved for the other system be the same. Examplesof physical transmission parameters that may differ include but are notrestricted to OFDM/OFDMA sub-carrier spacing, symbol time, and cyclicprefix (CP) duration.

In the example shown in FIG. 4, the other system operates with a channelbandwidth that is half of the bandwidth of the current system. As can beeasily seen from FIG. 4, there is no restriction in terms of thebandwidth needed by the other system relative to the bandwidth used bythe current system; the bandwidth of the other system may be smaller,equal to, or larger than the bandwidth of the current system.

In the example shown in FIG. 4, the other system operates with a channelwith its center offset from the center frequency of the channel used bythe current system. As can be easily seen from FIG. 4, there is norestriction in terms of the relative centering of the channel bandwidthused by the other system and the center of the channel bandwidth used bythe current system; the center of the channel bandwidth used by theother system may be above, the same as, or below the center of thechannel bandwidth used by the current system. There is also norestriction that the channel bandwidth used by the other system fallentirely within the channel bandwidth of the current system; there maybe any part of the channel bandwidth of the other system that fallsoutside the bounds of the channel bandwidth used by the current system.

In the example of FIG. 4, the other system is a TDD system that operateswith alternating downlink subframes, 410 and 412, and uplink subframes,411 and 413, with a frame comprising exactly one downlink subframefollowed by one uplink subframe with frame duration of 5 ms. As can beeasily seen, the directionality of transmission by the other systemwithin reserved subframe durations is not significant to the allocationrequirements for the reserved subframe durations within the currentsystem. The pertinent information of the other system includes theminimum periodicity of the reserved subframes and if applicable, anyrelative timing requirements between multiple reserved subframes withinthis minimum period. The periodicity of reserved subframes required bythe other system is defined in terms of the interval between tworeference reserved subframe durations, as represented by reservedsubframe durations 410 and 412 in FIG. 4. The frame time of the currentsystem should be selected as an integer multiple of the minimum periodof reserved subframe durations required by the other system. In thisway, the relative positions of the reserved subframe durations withinthe frame time of the current system remain fixed, thereby avoiding anyissues with reserved subframe durations conflicting with any periodicframe control information required by the current system. Given thisguideline for the setting of the frame duration of the current systemrelative to the periodicity requirements of reserved subframes of theother system, one can see that the choice of a 10-ms frame duration forthe current system in the example of FIG. 4 given that the reservedsubframe durations for the other system are repetitive at a 5-msinterval is a suitable choice; the reserved subframe durations fordownlink subframes of the other system remain at the same relativepositions within the 10-ms frame of the current system and thereby helpavoid any contention between the reserved subframe durations for theother system and the Frame Sync and Control signal 405 at the beginningof the 10-ms frame of the current system. As can be seen from theexample of FIG. 4, some variability can be accommodated in the relativeintervals between other reserved subframes, 411 and 413, that fallbetween the reference reserved subframes, 410 and 412, and thesereference reserved subframes.

FIG. 5 is an illustration of another exemplary method for the support ofspectrum sharing with another system based on otherTime-Division-Multiplexed (TDM) based transmission technologiesaccording to an embodiment of the invention. This method is mostapplicable to scenarios in which the other system requires reservationof a channel bandwidth that does not fully overlap with the channelbandwidth of the current system, thereby not requiring the entirebandwidth of the current system to be reserved for the other system whenrequired. This method only applies when the current system is based onOFDMA technology since OFDMA technology can make use of a subset of thesub-carriers at any time.

It is noted firstly that the method of FIG. 5 is similar in manyrespects to the basic method of spectrum sharing of FIG. 4 and that havealready been described in connection with the description of thatmethod. Therefore, the method of FIG. 5 is only described with respectto those aspects in which it is different from the basic method of FIG.4.

As shown in FIG. 5, this method utilizes the concept of physicalresource allocation based on a rectangular area within thetwo-dimensional OFDMA signal—the two dimensions being time andfrequency. Such a physical resource allocation is often known as anOFDMA region.

One aspect of the system is the ability to allocate OFDMA regions ofvarying lengths in both the time and frequency dimensions in bothdownlink and uplink subframes. The edges of the rectangular OFDMA regionare confined to fall within the frequency and time boundaries of asubframe.

One difference between the basic spectrum sharing method of FIG. 4 andthe more flexible method of sharing of FIG. 5 is that the reservedresources for the other system is defined in terms of subframe durationsin the basic method whereas the reserved resources for the other systemis defined in terms of OFDMA regions in the more flexible method.Therefore, in the more flexible method, the current system is allowed tomake use of any sub-carriers of the OFDMA signal that are not requiredby the other system during those intervals in which reservations ofsub-carriers are required for the other system. Another way to statethis difference is that the reserved areas for the other system in thebasic method appear as separate subframes within the current systemwhereas the reserved areas in the more flexible method appear as OFDMAregions within subframes of the current system. This lattercharacteristic of the more flexible method is shown in FIG. 5 where theOFDMA regions (510, 511, 512, 513) that are reserved for the othersystem are situated within subframes 504 within the current system.

Similarly to the basic method in FIG. 4, the more flexible method inFIG. 5 also has no restriction that the channel bandwidth used by theother system falls entirely within the channel bandwidth of the currentsystem; any part of the channel bandwidth of the other system may falloutside the bounds of the channel bandwidth used by the current system.In this latter case, the size of the OFDMA region reserved for the othersystem is determined by the amount of overlap of the channel bandwidthof the other system with the channel bandwidth of the current system.

Special placement considerations may be required if the reserved OFDMAregion for the other system falls within a downlink subframe within thecurrent system. This is due to the possibility of subframe controlinformation being present within the subframe. If present, this subframecontrol information typically resides at the front (earliest time) ofthe subframe. If this is applicable, the reserved OFDMA regions for theother system must not be situated at the front of downlink subframes forthe current system. This consideration is shown in FIG. 5 where thereserved OFDMA regions 510 and 512 for the other system are not situatedwithin the first unit subframe time in downlink subframes.

FIG. 6 provides a view of the frame for the same example scenario asFIG. 5 but from the perspective of the current system only. The figureshows that the reserved OFDMA regions for the other system appear asNULL regions in the current system, a NULL region being a frequency-timearea where there are no transmissions, uplink or downlink, from thecurrent system.

FIG. 7 illustrates how the method of frame control based on FramePartitions as described above can be simply extended to support ascenario where one or more secondary carriers are also assigned asresources available to the BS for communications over the air interface.A secondary carrier 701 may or may not be adjacent to the primarycarrier 700, and the resources of one or more of these secondarycarriers together with the resources of the primary carrier constitutethe available resources for the Base Station (BS).

In the extended method for multi-carrier support of FIG. 7, controlinformation exists only on the primary carrier 700. Besides the minimumcontrol information already described above for the primary carrier 700,an additional set of control information 714 provides control oftransmissions and resource allocations in Frame Partitions located on asecondary carrier. At a minimum, each set of Frame Partition controlinformation 714 for a secondary carrier includes the location and sizeof the secondary carrier, such as in terms of center frequency andbandwidth, respectively, or alternatively summarized by an Identifierfor the secondary carrier where the location and size information forthe secondary carrier have been previously associated with suchIdentifier, the locations, size and directionality of each subframe withconsiderations for such information being the same as for the primarycarrier 700 as discussed above, and the location, sizes and MSassignments of data transmissions for downlink subframes and resourcesfor UL data transmissions for uplink subframes.

Also in the extended method for multi-carrier support of FIG. 7, aparameter T_(f,offset) 721 is introduced that represents a time delayintroduced between the start of Frame Partitions on a secondary carrierand the associated Frame Partitions primary carrier. Such offsetrepresents time allowed for the MS to receive and process the FramePartition control information for the secondary carrier 714 from theprimary carrier 700, and if applicable, to switch transmit and receiveoperation to the secondary carrier 701. T_(f,offset) may be designed asa fixed system parameter or as a configurable parameter on a system-wideor per-secondary-carrier basis. In the latter case, the value of theparameter(s) may be included in system broadcast information to MSsbeing served by the BS.

FIG. 8 further illustrates how the exemplary method of multi-carriersupport on a BS can be applied to Frequency Division Duplex (FDD)operation. In this special case of multi-carrier operation of a BS, themethod of Frame Partition control at the primary carrier 800 and for thesecondary carrier 801 is identical to that described for generalmulti-carrier operation as described above with the constraint that allsubframes on the primary carrier 800 have a downlink directionality andall of the subframes on the secondary carrier 801 have an uplinkdirectionality.

Also in the exemplary method of FDD support of FIG. 8, the parameterT_(f,offset) 821 should be designed to be configurable on aper-secondary-carrier basis so that the value of the parameter can beset appropriately depending on whether only full FDD MSs are supportedor half-duplex FDD (H-FDD) MSs need to be supported also. H-FDD MSs donot transmit and receive at the same time. In the H-FDD case, sufficientdelay must be introduced by T_(f,offset) to allow sufficient non-overlapof the associated Frame Partitions between the primary carrier 800 andthe secondary carrier 801 so that downlink and uplink transmissions ofsufficient sizes can be performed to an H-FDD MS. For example, the FramePartitions may be set equal in size and the delay T_(f,offset) may beset to the size of the Frame Partition to essentially provide analternating pattern for a particular Frame Partition between the primaryand secondary carriers. If only full FDD MSs are supported on aparticular BS, the value of T_(f,offset) may be set substantiallyshorter since the MS can receive on the primary carrier 800 and transmiton the secondary carrier 801 simultaneously; in this case, time needonly be allotted for the MS to receive and process the Frame Partitioncontrol information 814 for the secondary carrier. A shorter value ofT_(f,offset) allows faster exchanges of data between a BS and MS, whichis especially relevant for control signaling exchanges—this can improveperformance of certain operations that benefit substantially from fastsignaling exchanges, such as Hybrid Automatic Repeat Request (HARQ)operation.

Another embodiment of the present invention describes a new approach todefine a proposed IEEE 802.16m standard (16m) frame structure withlegacy support for the IEEE 802.16e standard (16e) frame structure.

The proposed IEEE 802.16m standard may be important in the future andthe 16m frame structure needs to have an adaptable, evolvablefoundation. However, the legacy 16e frame structure imposes constraintsthat limit its adaptability. Thus, it is desirable to design the 16mframe structure to minimize degradation to 16m performance while servinglegacy 16e mobile stations on the same carrier. Furthermore, it isimportant to avoid two different 16m designs: one for pure 16m basestation (BS) and the other for 16m BS with 16e legacy support.

According to an embodiment of the invention, the new approach to 16mframe design comprises the following: (1) start with frame designtailored to meet 16m requirements (e.g., shorter delay, lower controloverhead, etc.); (2) add enough flexibility to allow frame partitioningand timing to fit legacy 16e frame requirements; and (3) fit legacy 16eframes and subframes into the 16m frame structure by appropriateresource reservation (16m frame structure elements and control are thesame regardless whether the 16m frame structure provides legacy supportor not).

An exemplary definition of an OFDM/OFDMA frame operating in TimeDivision Duplex (TDD) mode in accordance with one embodiment of theinvention is shown in FIG. 1. According to an embodiment of theinvention, the 16m frame structure provides greater flexibility insetting subframe parameters. First, frame duration is not tied to thenumber and direction of subframes. Second, frame duration is also nottied to meeting Quality of Service (QoS) delay requirements. Third,tradeoff between capacity and delay can be controlled via subframesettings. This flexibility in setting subframe parameters allows easyadaptation of many different scenarios. For example, alternating shortsubframes may be used for bi-directional real-time traffic.

The 16m frame structure has a 16m-specific preamble in the Frame Sync &Control signal. The Frame Sync & Control signal contains at leastcontrol parameters applicable to entire frame, and may contain controlinformation for subframes within the frame. The control information forsubframes may also be distributed in subframes.

Flexibility is an important aspect in 16m frame design. According to anembodiment of the invention, the parameters in the 16m frame structureare dynamically configurable. The 16m frame structure may have a longerframe compared to legacy 16e frame. However, longer frames do not equateto longer subframes, and frame duration and subframe duration are asindependent as possible. Subframes are distinguished by a direction anda set of physical (PHY) level properties. Most PHY properties areallowed to change from subframe to subframe.

FIG. 9 illustrates legacy 16e support in a 16m frame structure accordingto an embodiment of the invention. According to this embodiment of theinvention, the 16m frame structure 900 retains many of the attributes ofthe flexible frame depicted in FIG. 1. In addition, as shown in FIG. 9,certain NULL subframes 904 in the 16m frame are reserved for legacy 16euse. There are no 16m transmissions in the time durations of those“NULL” subframes 904. These time durations are reserved for use bysubframes 910, 911, 912 and 913 of the legacy 16e frame.

The 16m frame has its own preamble which is ideally orthogonal to theexisting preamble for legacy 16e. Legacy 16e MSs would acquire framesynchronization with legacy 16e preamble while 16m capable MSs wouldsynchronize to the new 16m preamble.

There is a fixed relative offset between the start of 16m frame and thestart(s) of legacy 16e frames that reside within the time duration ofthe 16m frame. This can be achieved by setting 16m frame duration to bean integer multiple of the embedded legacy 16e frame duration.

The parameters of OFDMA physical layer (PHY) in the 16m subframes may bedifferent from those in legacy 16e subframes. Radio resource managementis provided for determining what proportion of radio resources areavailable for 16m data transmission vs. legacy 16e data transmission.

In accordance with one embodiment of present invention, the 16m framedesign is not unnecessarily constrained by legacy 16e support. In oneembodiment, a new 16m frame structure is defined to satisfy the 16mrequirements with respect to frame structure. Legacy 16e support istreated as a separate frame structure embedded in the 16m frame, and the16m frame control is consistent while operating with or without legacy16e sharing. Accordingly, the 16m frame structure accommodates legacy16e support without being limited by its constraints.

In order to maximize the advantages for 802.16m, another embodiment ofthe invention provides a frame structure having the most flexibility tomeet 802.16m requirements.

Legacy support is then added as independently as possible into this newstructure. Approaching the 802.16m frame structure design this wayprovides several advantages over starting from the legacy framestructure and adding 802.16m support into the legacy frame structure,including: (1) minimizing the impact of the legacy frame structure onthe 802.16m frame structure; (2) minimizing the degradation to the802.16m performance while serving legacy 16e mobile stations on the samecarrier; (3) allowing 802.16m operation to be consistent whetheroperating with or without legacy support enabled; and (4) allowing an802.16m MS to operate in the same manner when being served by an 802.16mBS with or without legacy support enabled. In one embodiment, the802.16m frame structure does not tightly couple parameters that shouldbe controlled independently. Such parameters include: maximum time foropportunity to transmit in opposite direction; minimum time betweenframe synchronization opportunities; and parameters for schedulingrelevance timeframe.

The 16m frame structure in accordance with this embodiment of theinvention also provides a consistent base frame structure and framestructure elements that could be applied to all required radio carrieroperating scenarios: TDD, FDD, half-duplex FDD (H-FDD), andmulti-carrier.

FIG. 10 illustrates the basic format and major elements of the proposedIEEE 802.16m frame according to one embodiment of the invention. Thisformat provides sufficient flexibility to allow this base framedefinition to be catered to various operating scenarios, such as to meetvarying minimum traffic QoS requirements or for different radio carrierconfigurations, different duplexing modes or multi-carrier operation.However, as the design matures, some of the flexibility may besacrificed as a reasonable tradeoff to reduce frame control overhead.

Referring to FIG. 10, the base frame definition includes five elementsin hierarchical order: frame; frame partition; subframe, subframepartition; and unit subframe. The base frame definition 1100 includes: aframe duration (T_(frame)) 1007, a Frame Sync and Control signal 1002,one or more downlink subframes 1003 and 1004 of varying durations, oneor more uplink subframes 105 and 106 of varying durations. A subframecomprises an integer number of unit subframe durations (T_(u-sub)) 1001.Adjacent subframes may provide communications in the same direction,such as 1005 and 1003/1004, or may provide communications in oppositedirections, such as 1003/1006. The first subframe 1008 is a downlinkframe and contains the Frame Sync and Control signal 1002.

Also shown in FIG. 10, consecutive subframes within the base frame 1000are grouped into Frame Partitions 1010. A frame may be comprised of aone or more Frame Partitions and the Frame Partitions may be ofdifferent durations. A Frame Partition provides more localized controlof subframe structure within a frame. Another benefit of FramePartitions is the flexibility to shorten the scheduling window totimeframes that are shorter than the duration of a frame, which canbenefit the scheduling of time-critical traffic.

A Frame Partition 1010 is comprised firstly of a downlink subframe whichcontains a Frame Partition Control data block 1011 that is situated at aknown location in the subframe (for example, located at the upper leftcorner of the frequency-time space of this first downlink subframewithin a Frame Partition as shown in FIG. 10). Following the firstdownlink subframe, there may be 0 or more other subframes of varyingdurations and various directionalities that comprise the FramePartition. The maximum duration of any Frame Partition is constrained bythe number of unit subframe times remaining from the start of the FramePartition to the end of the frame.

The Frame Partition Control 1011 defines the subframe structure of theFrame Partition. This subframe structure definition includes at leastthe following control information: 1) pointers to the time location ofthe start of each subframe that follows the first downlink subframewithin the Frame Partition, 2) the directionality of each subframe(i.e., whether the subframe is used for downlink or uplinktransmissions) that follows the first downlink subframe within the FramePartition, 3) the time duration T_(sub) of each subframe, and 4) apointer to the start of the next Frame Partition in the frame.

A subframe is comprised of one or more subframe partitions (not shown inFIG. 10. As described above, a subframe partition is comprised of one ormore unit subframes of identical or compatible configurations, andtherefore, is an integer number of unit subframes in length. The numberand lengths of subframe partitions are set on a subframe by subframebasis based on what may be the best configuration for the MS and trafficbeing serviced at a particular time. A subframe partition ischaracterized by a length and properties of its constituent unitsubframe(s).

A unit subframe may contain one or more (typically several) OFDMAsymbols periods and one or more idle times across all subcarriers. FIG.11 provides some illustrative examples of unit subframe formats that canbe applied to DL subframe partitions. Example (a) in the FIG. 11 shows aunit subframe 1101 which is maximally filled with OFDM symbol periods1111, 1112, . . . 111 n (that is, with ideally no idle time). This typeof subframe would typically be used in all cases except as the last unitsubframe of the last subframe partition in a DL subframe for the case ofTime Division Duplex (TDD) operation or as the first unit subframe inthe first DL subframe partition in the first subframe of a frame.Example (b) in FIG. 11 shows a unit subframe 1102 containing sufficientidle time 1199 for direction switching at the end of the unit subframeto be used as the last unit subframe in the last subframe partition of aDL subframe in TDD mode. Example (c) in FIG. 11 shows a unit subframe1103 containing a Sync Symbol 1131 at the beginning of the unitsubframe. Unit subframe 1103 would be one that can be applied where asynchronization signal is required in a subframe partition.

According to another embodiment of the invention, a similar set of unitsubframe structures as those shown in FIG. 11 can be applied to ULsubframe partitions. The exact set of unit subframe formats will dependon the definition of the OFDMA symbol parameters and unit subframelength, which determines the fit of symbol periods within the unitsubframe.

The base frame structure illustrated in FIG. 10 is directly applicableto TDD operation. The main additional consideration for TDD operation isthat the frame and subframe boundaries and subframe directions should bealigned between BSs in the neighborhood in order to minimizeinterference issues.

Support for MSs that conform to the WirelessMAN-OFDMA Reference Systemby an IEEE 802.16m BS is provided by the time-division multiplexing(TDM) of subframe partitions of the 802.16m frame with sections of DLand UL subframes of the legacy 16e OFDMA frame. FIG. 12 illustrates anexemplary method of legacy 16e frame support via TDM according to anembodiment of the invention.

Some aspects of the TDM operation with legacy support are describedbelow. First, the IEEE 802.16m frame 1200 contains a separate Preamble1202 for IEEE 802.16m operation that is orthogonal to the legacyWirelessMAN-OFDMA Preamble 1212 in order to achieve virtuallytransparent operation between MSs operation in IEEE 802.16m mode versusthose operating according to the WirelessMAN-OFDMA Reference System. Thedetailed definition of the new Preamble is to be determined.

Second, the length of the IEEE 802.16m frame 1200 is set to be aninteger multiple of the legacy WirelessMAN-OFDMA frame length of 5milliseconds. This allows a fixed offset to be maintained between thestart of the IEEE 802.16m frame and the starts of one or more legacyWirelessMAN-OFDMA frames that overlap within the IEEE 802.16m frame.

Third, the IEEE 802.16 frame 1200 uses NULL subframe partitions 1204 inthe frame to reserve parts of the frame for the legacy WirelessMAN-OFDMAframe 1210. A NULL subframe partition is defined to be one in which noIEEE 802.16m transmissions are generated either by the BS or MS. Forexample, the time durations of NULL subframe partitions 1204 arereserved for use by parts 1213 and 1214 of the legacy 16e frame 1210.

Fourth, the IEEE 802.16 frame uses existing mechanisms provided by thelegacy WirelessMAN-OFDMA Reference System to notify legacyWirelessMAN-OFDMA MSs of gaps in the DL and UL subframes that arereserved for legacy use. Such gaps may be located at any symbol offsetwithin a DL or UL subframe including being inserted in the middle of aDL or UL subframe to reduce the delay impact on IEEE 802.16m operation.An example of this is shown in FIG. 12 where the DL subframe 1215 of thesecond legacy WirelessMAN-OFDMA frame is fragmented into two by theinsertion of a pair of IEEE 802.16m subframes 1205 within the legacy DLsubframe timeframe.

According to an embodiment of the invention, an extension of the baseframe structure of FIG. 10 for operation on multiple simultaneouscarriers on a BS provides the FDD frame structure as a specificsub-case. This extended multi-carrier frame structure with specificapplication to FDD is illustrated in FIG. 13.

The FDD frame structure shares the same frame structure elements as theTDD frame structure with the identical elements and control appearing inthe DL carrier 1300, which is considered the primary control carrier.Besides providing control of the frame structure and radio resourceallocation within the DL carrier itself, as a primary control carrier,it also provides the frame structure and radio resource allocationcontrol for the UL carrier 1301, which is considered a secondary carrierthat is bound to the primary control carrier.

The type of control information provided by the primary control DLcarrier pertaining to the secondary UL carrier may be grouped into twocategories: 1) semi-static and 2) dynamic. The semi-static controlinformation may be configurable and generally remains constant forextended periods of time (generally until some system configuration ischanged) and so may be communicated as system broadcast information. Thedynamic control information generally changes from one instance of theelement to the next to which the control information pertains.

The semi-static information may include the following FDD frame controldata: the location and size of the secondary UL carrier 1301, themapping of the carrier to a carrier identifier; the time offset,T_(f,offset) 1321, from the start of the frame at the primary control DLcarrier to the start of the same frame at the secondary UL carrier. Thetime offset T_(f,offset) 1321 provides some allowance for the MS toreceive and process control information at the primary carrier before itneeds to be applied at the secondary UL carrier. To support half-duplexFDD (H-FDD) operation, this offset 13121 may also include allowance forchannel switching from the primary control DL carrier to the secondaryUL carrier and for ensuring sufficient non-overlap time between theframe partition at the primary control DL carrier and the same framepartition at the secondary UL carrier. There is a separate T_(f,offset)for each secondary carrier.

The dynamic control information is primarily associated with each framepartition and so to support FDD (and generally multi-carrier) operation,a new set of control data for the associated frame partition at thesecondary UL carrier is included in the Frame Partition Control signal1311 sent by the primary control DL carrier 1300 for each framepartition 1320.

The frame partition control signal 1311 for the secondary UL carrier1301 includes the subframe configuration within the frame partition. ForFDD sub-case of multi-carrier operation, all subframes on the primarycontrol carrier are downlink and all subframes on the secondary carrierare uplink. Because of this, there is generally no need for more thanone subframe per frame partition since the primary characteristic of asubframe is its directionality.

The frame partition control signal 1311 also includes the subframepartition configuration within each subframe in the frame partition, theconfiguration and assignment of data allocations within each subframepartition, and the time offset, T_(fp,offset), that specifies the offsetof a frame partition on the primary control DL carrier to the associatedframe partition at the secondary UL carrier. Having separate timeoffsets for each frame partition allows the frame partitions at thesecondary carrier to be a different length from the associated framepartition at the primary control DL carrier.

It is desirable that the design of 802.16m enables 802.16 to be acost-effective, global, and competitive technology well into the future.Meeting such needs requires some balancing between how 802.16m will beconstrained by the requirement to support legacy MSs while meeting theneeds as a global IMT-Advanced technology. One of the foundations of802.16m technology will be the configuration of the OFDMA technologythat serves as the base physical layer multiple access and transmissiontechnology for 802.16m. In order for 802.16m to be such acost-effective, competitive, global technology, a new approach to OFDMAconfiguration is adopted in accordance with one embodiment of theinvention, wherein the subcarrier spacing is fixed to a value thatserves well the radio environments that 16m is intended to operate in,and is highly compatible with available and potential future carrierbandwidths. According to one embodiment of the invention, the physicallayer of 16m is based on a fixed subcarrier spacing of 12.5 kHz. Therationale for this approach and the selection of this particular spacingand the issues with retaining the current OFDMA parameters are describedin detail below.

The IEEE 802.16m System Requirements Documents (SRD) requires that IEEE802.16m shall meet the IMT-Advanced requirements. Furthermore, allenhancements included as part of IEEE 802.16m should promote the conceptof continued evolution, allowing IEEE 802.16 to maintain competitiveperformance as technology advances beyond 802.16m.

On the other hand, the IEEE 802.16m SRD also requires that IEEE 802.16mshall provide continuing support and interoperability forWirelessMAN-OFDMA Reference System which is defined as system compliantwith the capabilities set specified by WiMAX Forum Mobile System ProfileRelease 1.0. For example, based on the backward compatibilityrequirements, 802.16m BS shall support 802.16m and legacy MSs while bothare operating on the same RF carrier.

But there are a lot of problems existing in current legacy systemdesign. Some of them have an unfavorable impact on systemimplementation, network deployment and equipment cost. So theinheritance of legacy system's drawbacks shall be prevented whendesigning 802.16m system.

OFDMA numerology is the base of OFDM technology and directly affects theframe structure design, which is one of the basic elements of thePhysical Layer. The section below describes some problems caused byOFDMA numerology which is used by legacy system and their effect oncurrent legacy system.

Problem No. 1 is that legacy numerology cannot ease the pain of legacysupport. The legacy systems with 5/10/20 MHz, 3.5/7 MHz and 8.75 MHzbandwidths have different subcarrier spacing values which are derivedbased on different series bandwidths, and therefore different sets ofsampling frequencies. Such incompatible sampling frequency sets imposeunnecessary complexity for equipment to support the various bandwidths.Based on the legacy support requirements, 802.16m BS shall support802.16m and legacy MSs while both are operating on the same RF carrier.However, there are three sets of legacy numerology in the 16e (or WiMAX)deployment, namely 5/10, 7/14, and 8.75. It is desirable to support themall to ensure global roaming compatibility with common equipment anddevices. However, these legacy systems not only have differentnumerology parameters such as subcarrier spacing, they are often locatedin different frequency bands. These are tremendous challenges in the 16mdesign to support legacy systems.

The traditional argument is that 16m system can adopt the existinglegacy numerology, and can support the 16e system without much pain.However, this approach will compromise 16m performance. Assuming that16m OFDMA design is based on the numerology that already exists in802.16e, there are two options under this approach.

Option 1: Take the different sets of numerology as they are. The 16m MSwill support all legacy sampling rates and subcarrier spacings even ingreen field deployment (where legacy support is turned off). This meanssupporting different bandwidths and different numerology sets for globalroaming. This option could be the easiest way to achieve legacy support.However, the existing Long Term Evolution (LTE) and Ultra MobileBroadband (UMB) designs have each already adopted a single set ofnumerology, but the 16m design is going to remain with 3 sets ofnumerology for 5/7/8.75 Mhz system bandwidths. With the requirement tosupport 16m devices global roaming, it would be difficult to reduce thecosts of 16m with multiple sets of numerology. Furthermore, there arequite a few problems in today's 16e numerology (stated in detail below).For example, it is unclear how 16m will handle 6-MHz and 12-MHz systembandwidths which have been defined in 700 MHz and other bands. Creatinga 4^(th) set of numerology for them is not a good option. It is hard topredict what other bandwidths will be allocated for the IMT-AdvancedBands. Continuing adding new sets of numerology will continue to requiremore costly and complex designs for future 16m. Other competingtechnologies are using single sets of numerology and design to supportdifferent system bandwidths in different bands to achieve globalroaming, and 16m would not have much competitive edge. Thus, option 1 isnot very promising.

Option 2: Take one of the legacy sets of numerology (for example, thepopular 5/10 MHz). The MS will still need to support different sets ofnumerology for legacy support—namely 7/14 MHz and 8.75 MHz. The argumentof sharing only one set of numerology between 16m and 16e design will nolonger be true. At least we cannot have one set of numerology for 16mdesign for global roaming. Since a 16m MS design would need to supportmultiple sampling base frequencies for legacy support anyway, such asproviding support for both 16m (2.5 GHz, 10.9375 kHz) and 16e (3.5 GHz,7.8125 kHz) using a rate change filter with one crystal or via separatecrystals, then there is no difference in design complexity regardless ofthe subcarrier spacing used by 16m—either 10.9375 kHz or othersubcarrier spacing such as 12.5 kHz. However, as discussed below, thereare many issues with using the 10.9375 kHz subcarrier spacing.

Problem No. 2 is that legacy numerology has low spectral efficiency dueto unused guard subcarriers. The numerology based on a typical legacy16e design can be found in Table 310 a of IEEE 802.15e 2005. Out of 914subcarriers that fall into the 10 MHz bandwidth, there are only 840subcarriers that can be used to transmit information—8.8% of thebandwidth is wasted. Furthermore, the bandwidth occupied by the 914subcarriers does not fully fill the 10-Mhz carrier bandwidth. Thefollowing is the formula on how to calculate the maximum frequencyefficiency:

$\begin{matrix}{n_{Efficiency} = \frac{R_{Modulation} \times n_{UsedSubcarriers}}{T_{symobol} \times {BW}_{System}}} & ( {{{Eq}.\mspace{14mu} 2}\text{-}1} )\end{matrix}$

where R_(Modulation) is modulation rate (e.g., 4 for 16QAM),n_(UsedSubcarriers) is number of used subcarriers within the nominalsystem bandwidth, T_(symobol) is symbol period, and BW_(system) is thenominal system bandwidth.

Let's set cyclic prefix (CP)=0 to calculate the maximum n_(Efficiency)of the system.

$\begin{matrix}{T_{symobol} = \frac{1}{f_{\Delta}}} & ( {{{Eq}.\mspace{14mu} 2}\text{-}2} )\end{matrix}$

where f_(Δ) is subcarrier spacing.

BW _(system) ≧n _(MaximumSubcarriers) ×f _(Δ)  (Eq. 2-3)

where n_(MaximumSubcarriers) is the maximum number of subcarriers that anominal system bandwidth can have.

Let's substitute Eq. 2-2, and Eq. 2-3 into Eq. 2-1, we can conclude asfollowing:

$\begin{matrix}{n_{Efficiency} \leq \frac{R_{Modulation} \times n_{UsedSubcarriers}}{n_{MaximumSubcarriers}}} & ( {{{Eq}.\mspace{14mu} 2}\text{-}4} )\end{matrix}$

The frequency efficiency is proportional to the number of usedsubcarriers number over the maximum number of subcarriers within thesystem bandwidth. We can see if we can use the 73 Guard Subcarriers(n_(MaximumSubcarriers)−n_(UsedSubcarriers)=914−841=73) and 1 DCsubcarrier to transmit data and divided it by the maximum number ofsubcarriers of 914, the new 16m system can be immediately 8.8% moreefficient. The proposed 16m numerology described in one embodiment ofthe invention allows all subcarriers to be used for data transmissionwithout Guard Subcarriers since the subcarrier spacings between adjacentabutting carriers are aligned. This makes operation with the proposed16m numerology to be 8.8% more efficient by design when compared to PUSCoperation with the existing 16e numerology. When the operator bandwidthhas sufficient guard band around a carrier, then the 8.8% would not bewasted.

Problem No. 3 is that legacy numerology incurs capacity loss inmulti-carrier deployment due to the non-aligned subcarriers in adjacentcarriers. With the current WirelessMAN-OFDMA Reference System, thecenter frequencies of carriers are located on a 250-kHz raster from thespectrum band edge. The 250-kHz raster is commonly used since it dividesevenly into all carrier bandwidths (which are typically set in multiplesof 0.5 or 1 MHz), and is fine enough to allow flexibility in fine-tuningthe location of carriers within spectrum bands or blocks within theband, but yet is somewhat coarse to reduce the number of potentialcenter frequency locations (and thereby limit MS search times foroperating carriers). Since the 250-kHz raster can be evenly divided intothe available and typical carrier bandwidths, adjacent carriers can beplaced abutting to each other and thereby maximize the usage of theavailable spectrum. An example of this type of RF deployment isillustrated in FIG. 14 where two adjacent 5-Mhz carriers are deployedwith legacy subcarrier spacing.

Also shown in FIG. 14 is the issue with using the legacy subcarrierspacing of 10.9375 kHz for the 5 and 10-MHz bandwidths in thisscenario—since there is not an integer number of subcarriers from thecarrier center frequency to the carrier edge, the subcarriers are notaligned between the adjacent carriers. The nature of OFDM operation issuch that transmissions on a subcarrier do not introduce interferencepower at points that are an integer number of subcarrier spacings fromthe transmitting subcarrier but do cause interference power betweenthese points. Therefore, subcarriers not being aligned between adjacentcarriers means that interference from transmissions near the edge of onecarrier causes excessive interference to subcarriers near the edge ofthe adjacent carrier if not properly addressed. In the design of thelegacy WirelessOFDMA-MAN Reference System, this issue was addressed viathe combination of two approaches: 1) the reservation of a number ofsubcarriers at the carrier edge as unused guard subcarriers so that someinterference reduction is achieved by natural decay of the transmittedsignal power with increasing frequency separation, and 2) the use of atransmit filter to further reduce the interference power to the adjacentcarrier to an acceptable level. Both of these approaches incuroverhead: 1) loss of capacity of between 5% to more than 8% due to guardsubcarriers, and 2) implementation cost/complexity due to requirement oftransmit filter. Both of these overheads of the legacy system can beeliminated by simply aligning the subcarriers between the adjacentcarriers.

Problem No. 4 is that legacy numerology lacks multi-carrier scalabilityfor multi-carrier deployment. Service providers often prefer scalabledeployment plan in which more carriers are launched as the businessgrows. The incompatible subcarrier spacing unnecessarily restricts theefficiency and flexibility for 1.25 MHz series (5, 8.75, 10, 20 MHz) and3.5 MHz series (3.5, 7, 14 MHz) to work in multi-carrier mode, with thecarriers being of the same or a mixture of different system bandwidths.FIG. 15 illustrates an exemplary operation of multi-carrier deploymentwith guard bands. FIG. 16 illustrates an exemplary operation of mixedsystem bandwidths multi-carrier deployment. If the carriers are operatedas adjacent carriers as illustrated in FIGS. 15 and 16, inter-carrierinterference due to incompatible subcarrier spacings necessitates thepresence of guard subcarriers as was discussed above. In addition, themultiple carriers cannot be operated as an overlay of several multiplebandwidths onto a common aggregate bandwidth (common FFT) in order tosupport devices of different bandwidth capabilities at the sametime—this feature is important for supporting devices with verydifferent cost, complexity and throughput requirements on a common airinterface (e.g., from low-rate, low-cost remote datacollection/monitoring devices to high-end multimedia devices). Thismulti-carrier mode is illustrated in FIG. 17, which illustrates anexemplary operation of mixed bandwidths multi-Carrier deployment withoutguard bands.

In one embodiment of the invention, 16m uses 12.5 kHz as the subcarrierspacing, and lines up with different rasters in different frequencybands and the subcarrier spacings between adjacent carriers are aligned.Therefore, this subcarrier spacing allows multi-carrier deployment withthe same or mixed of different system bandwidths to be readilysupported. This capability provides 16m a competitive advantage over UMBand LTE which cannot support multi-carrier deployment without guardsubcarriers between neighboring carriers, as shown in FIG. 17. Itdemonstrates great advantages in multi-carrier deployment and theeasiest way to achieve global roaming for different 16m devices.

Problem No. 5 is that changing raster to address Problem No. 3 causesother problems. A sufficient requirement to achieve the alignment ofsubcarriers between adjacent carriers is to define the raster as aninteger number of subcarrier spacings and to separate the centerfrequencies of adjacent carriers by an integer number of rasterspacings. There are two design approaches that can be taken to meet thisrequirement: (a) retain subcarrier spacing from the legacyWirelessOFDMA-MAN Reference System and define a new raster based on it;and (b) retain the existing 250-kHz raster and define a new subcarrierspacing for 802.16m.

There are issues with approach (a) described above. Legacy support isadversely affected since the centering of carriers for 802.16m will bedifferent from that for the WirelessOFDMA-MAN Reference System. Thismis-alignment of carriers is illustrated in FIG. 18. An importantcharacteristic to note from FIG. 18 is that the offsets between the twosets of carriers are not constant, which complicates the design andengineering of legacy support significantly. The offset in centerfrequencies resulting from the different rasters causes mis-alignment ofthe operating carrier bandwidth and of the subcarriers between thelegacy zones and the new 16m zones when they occupy overlappingfrequency spaces—an example of which is illustrated in FIG. 18. Having aseparate set of carrier center frequencies for 802.16m operation due toa different raster also adversely affects the time required for 802.16mMSs to search for available 16m or legacy service due to a doubling ofthe number of possible center frequencies that need to be searched.

Especially for the 10.9375-kHz subcarrier spacing that applies to5/10/20-MHz bandwidth operation, a raster cannot be defined consistingof an integer number of subcarrier spacings that also divide evenly intothe 5, 10 or 20 MHz bandwidths. For this case, there is only one rastervalue of 175 kHz that exists in the same raster value range as 250 kHzin which the raster can be defined in units of kHz (others are in muchfiner units such as in Hz or fractions of Hz); and it can be easily seenthat 175 kHz does not divide evenly into 5, 10, nor 20 Mhz. Given thissituation, there are only two ways in which the center frequencies ofadjacent carriers can be aligned to a multiple of rasters from thespectrum band edge: 1) introduce a gap between adjacent carriers asshown in FIG. 15 and FIG. 16, and 2) eliminate the need for a gapbetween adjacent carriers by truncating the effective bandwidth of thecarrier as shown in FIG. 17. In both cases, some spectrum wastage isnecessary.

Implementations are affected since a consistent centering of a carrieror a set of adjacent carriers within the same relative position within aspectrum band or block within a band cannot be defined—this may impactthe availability of low-cost generic parts in designs.

The issues noted above for approach (a) do not apply to approach (b)since for approach (b), by definition there will be an integer number ofsubcarrier spacings in the 250-kHz raster and as noted earlier, the250-kHz fits evenly within all carrier bandwidths that currently existfor 802.16. Using a subcarrier spacing that divides evenly into the250-kHz raster provides the additional benefit of being able to easilyaccommodate other possible future bandwidths that should be consideredin order to maximize the usage of allocated spectrum without incurringany of the issues related to approach (a). An example of the latterwould be to support carrier bandwidths based on a 6-MHz increment sincequite a few spectrum allocations in the U.S.A. for broadband wirelessservices are either 6 or 12-Mhz wide.

A potential drawback of approach (b) may be the need for an 802.16m BSto be able to switch between two subcarrier spacings dynamically whenoperating with legacy support enabled. The additional implementationcomplexity this incurs should be manageable since this type of dynamicswitching can be handled by straightforward designs, and the need tosupport multiple subcarrier spacings with the same hardware exist withthe WirelessMAN-OFDMA Reference System today if a BS is designed tosupport two or more of 5/10-MHz, 3.5/7-MHz, and 8.75-MHz operation. Inaddition, approach (a) also introduces disparate operation betweenlegacy zones and 802.16m zones due to a misalignment of carrierbandwidth and subcarrier spacings between the zones. The complexity ofaddressing this issue with approach (a) may be greater than simplyaddressing two subcarrier spacings between these zones as in approach(b).

Problem No. 6 is that a single subcarrier spacing of 10.9375 kHz isrequired to define all the used subcarriers for each system bandwidth.The used subcarrier number of each bandwidth needs a new definition withmodification needed in Problem No. 4. A new system profile is needed foreach new system bandwidth. Using a 12.5 kHz subcarrier spacing, allexisting bandwidth allocation in all frequency band classes can bedivided evenly. There is no a need to define used subcarriers for eachnew system bandwidth. Today, we know that 6 MHz and 12 MHz allocated in700 MHz Band and other Frequency Bands. It is also very hard for us topredict what other bandwidths will be allocated for the IMT-AdvancedBands. With a 12.5 kHz subcarrier spacing, we know exactly what the usedsubcarriers for these bandwidths are, and the 16m design will be forwardcompatible. When additional guard subcarriers are needed, the resourceblocks on the edge can be dropped to meet out of band emissionrequirements.

Problem No. 7 of the legacy numerology is that it has different numberof used subcarriers. For one given FFT size of legacy system, the valuesof the number of used subcarriers are different due to differentpermutation mode, even for the same channel bandwidth. For example, in alegacy system where the FFT size is 1024 and the channel bandwidth is 10MHz, the number of used subcarrier ranges from 841 to 865 with varyingbandwidth efficiency. This is a problem that can be prevented with anappropriate 802.16m frame structure design. With a common 12.5 kHzsubcarrier spacing, the used subcarrier number is well determinedwithout confusion.

On the one hand, as specified by Mobile WiMAX System Profile, only onetype of cyclic prefix (CP) exists in current legacy system, which is ⅛of useful symbol time.

Problem No. 8 is that legacy numerology uses a single cyclic prefix (CP)ratio for system deployment. Current legacy systems do not supportdifferent CP lengths for different BSs in the network, but only oneeffective CP value is used for all the BSs. Actually there are nomechanisms to allow a BS to change or configure the CP duration incurrent legacy systems. However, it is not suitable to use only one typeof CP length for different deployment environments. For example, in thescenario with severe multipath (i.e., larger delay spread), a longer CPshould be used to eliminate the ISI and ICI. But a simpler scenario withfewer multipath only requires a short CP in order to reduce overhead andtransmission power.

On the other hand, the CP length defined by current legacy systems is afraction of useful symbol time. But the CP duration should not bedependent on the useful symbol time, especially in current legacysystems where the useful symbol time changes between different samplingfrequency sets. It causes unnecessary overheads in most of thedeployment scenarios, and results in unnecessary reduction in frequencyefficiency.

Problem No. 9 is that a new 16m frame design based on legacy numerologyis not backward compatible with LTE frame structure in time. Due to theunequal symbol durations caused by multiple sets of existing legacynumerology, a 16m frame structure based on substructure boundaries thatare aligned to symbols of the legacy numerology is unsuitable. Thereforethe 16m unit subframe design (or equivalent term of “slot”) can not bealigned with the current LTE design. It can not be backward compatiblewith LTE Super-frame in time.

Now that 16m has been targeted to be adopted as an IMT-Advancedtechnology, it will inevitably co-exist with LTE side-by-side in thesame IMT-Advanced and IMT-2000 Bands. It will be a great disadvantage if16m cannot be deployed after LTE system has been deployed in the samefrequency band. It is most likely that LTE equipment will be deployedahead of 16m in the next few years, and the potential of 16m may beunnecessarily limited.

By changing 16m to adopt a 12.5 kHz subcarrier spacing, 16m design willbe more favorable to time aligned subframe design. The subframe can bedesigned to time aligned with current LTE multiple 0.5 ms slotsuperframe structure. It is important for 16m to co-exist with LTE andthe TD-SCDMA frame structure. It can be designed with PHY optimizationfor across RAT hand-off design, and be technically superior to existingLTE. The 16m design describe herein can become the technology candidateof LTE future evolution, and forms the base line technology forIMT-Advanced harmonization.

According to an embodiment of the invention, the IEEE 802.16m system hasthe following OFDMA numerology: (1) a subcarrier spacing of 12.5 kHz,(2) support for a new frame structure backward compatible to LTE, (3)multiple CP selections, and (4) a frame structure design time-alignedwith LTE.

FIG. 19 illustrates a 16m system having a subcarrier spacing of 12.5kHz. As shown in FIG. 19, the 12.5 kHz subcarrier spacing is applied forall the channel bandwidth, e.g., 5/10/20 MHz, 3.5/7/14 MHz and also 8.75MHz. The 12.5 kHz subcarrier spacing has a property of good trade-off ofmobility and frequency efficiency with CP overhead, and divides evenlyinto the 250-kHz channel raster. The sampling frequency of differentchannel bandwidths will be based on this subcarrier spacing andappropriate FFT size. It means that all the channel bandwidths will havethe same base sampling frequency. The mobile stations can roam todifferent carrier bandwidths in different frequency bands whileutilizing the same OFDMA parameter set—this feature is very crucial fora simplified coherent 4G standard and developing a healthy ecosystem.

The 16m numerology supports a new frame structure backward compatible toLTE. The existing 16e numerology will make it impossible to design aframe structure that will be backward compatible to LTE. The 16m with16e numerology will not be able to design sub-frame or slots that willtime aligned with LTE slots. Since 16m will be in IMT-Advanced, it willmake sense to be able to deployed side-by-side with LTE in the samefrequency band.

The 16m numerology supports multiple CP selections. Table 1 is anexemplary table of basic OFDM parameters with a 12.5 KHz sub-carrierspacing according to one embodiment of the invention. In accordance withone embodiment of the invention, three CP lengths based on 12.5-kHzsubcarrier spacing are provided and used for different radio scenarios.These three CP lengths are needed to adequately balance the requiredlength of CP with the loss of capacity due to the CP in order to servethe breadth of radio environments envisaged for 802.16m. These threetypes of CP are short CP with 2.5 us duration, which is typically usedfor very small cell deployments such as indoor, normal CP with 10 usduration which is typically used for outdoor urban and suburbanenvironments, and long CP with 15 us duration which is needed for thelarge delay spreads that may be encountered with large rural cells.

TABLE 1 Numerology with 12.5 kHz Subcarrier Spacing Parameter UnitParameter Values Channel Bandwidth (BW) MHz 5 6 7 8.75 10 12 14 20Sub-carrier Spacing (Δf) KHz 12.5 Sampling Frequency (Fs) MHz 6.4 12.812.8 12.8 12.8 25.6 25.6 25.6 FFT size 512 1024 1024 1024 1024 2048 20482048 Number of Used sub- 400 480 560 700 800 960 1120 1600 carriers(Nused) CP Short CP μs 2.5 Length Normal CP μs 10 (T_(CP)) Long CP μs 15

In accordance with one embodiment of the invention, the number of usedsubcarriers is independent of permutation mode. For all the types ofpermutation modes, with the same bandwidth, the number of usedsubcarriers is same. In accordance with another embodiment of theinvention, TDM mode is used for both downlink (DL) and uplink (UL) datatransmission for legacy system support.

The 16m numerology supports a frame structure design time-aligned withLTE. Table 2 is an exemplary table of basic unit subframe parametersthat are backward compatible with LTE slots according to one embodimentof the invention.

TABLE 2 Unit Subframe to Be Backward Compatible with LTE Slots ParameterUnit Parameter Values Channel Bandwidth (BW) MHz 5 7 8.75 10 14 20Sub-carrier Spacing (Δf) KHz 12.5 Sampling Frequency (Fs) MHz 6.4 12.812.8 12.8 25.6 25.6 FFT size 512 1024 1024 1024 2048 2048 Number of Usedsub-carriers 401 561 701 801 1121 1601 (Nused) CP Length Short CP μs 2.52.5 2.5 2.5 2.5 2.5 (T_(CP)) Normal CP μs 10 10 10 10 10 10 Long CP μs15 15 15 15 15 15 Long CP 2 μs 20 20 20 20 20 20 Sub-frame duration ms0.5 0.675 1 1.5 2 2.5 Number of Short CP (N_(S)) 6 8 12 18 24 30 OFDMNormal CP (N_(R)) 5 7 10 16 22 27 Symbols Long CP (N_(L)) 4 6 10 15 2026 Per Sub- Long CP 2 (N_(L)) 4 6 9 14 19 24 frame

In another embodiment of the invention, the physical layer of 16m isbased on a fixed subcarrier spacing of 25 kHz. Table 3 is an exemplarytable of basic OFDM parameters for a 25 series (25 KHz sub-carrierspacing) for mobility mode according to an embodiment of the invention.

TABLE 3 Numerology with 25 kHz Subcarrier Spacing Parameter UnitParameter Values Channel Bandwidth (BW) MHz 5 7 8.75 10 14 20Sub-carrier Spacing (Δf) KHz 25 Sampling Frequency (Fs) Mhz 6.4 12.812.8 12.8 25.6 25.6 FFT size 256 512 512 512 1024 1024 Number of Usedsub-carriers 201 281 351 401 561 801 (Nused) CP Length Short CP μs 2.52.5 2.5 2.5 2.5 2.5 (T_(CP)) Normal CP μs 10 10 10 10 10 10 Long CP μs15 15 15 15 15 15 Long CP 2 μs 20 20 20 20 20 20 Subframe duration ms0.5 0.675 1 1.5 2 2.5 Number of Short CP (N_(S)) 11 15 23 35 46 58 OFDMNormal CP 9 13 19 29 39 49 Symbols Per (N_(R)) Subframe Long CP (N_(L))8 11 17 26 35 44 Long CP 2 7 10 16 24 32 41 (N_(L)) Subframe Idle ShortCP μs 32.5 37.5 22.5 12.5 45 35 Time (TTG- Normal CP 50 25 50 50 50 50DL or TTG- Long CP 60 70 65 70 75 80 UL) Long CP 2 80 75 40 60 80 40

While various embodiments of the invention have been described above, itshould be understood that they have been presented by way of exampleonly, and not of limitation. Likewise, the various diagrams may depictan example architectural or other configuration for the invention, whichis done to aid in understanding the features and functionality that canbe included in the invention. The present invention is not restricted tothe illustrated example architectures or configurations, but can beimplemented using a variety of alternative architectures andconfigurations. Additionally, although the invention is described abovein terms of various exemplary embodiments and implementations, it shouldbe understood that the various features and functionality described inone or more of the individual embodiments are not limited in theirapplicability to the particular embodiment with which they aredescribed, but instead can be applied, alone or in some combination, toone or more of the other embodiments of the invention, whether or notsuch embodiments are described and whether or not such features arepresented as being a part of a described embodiment. Thus the breadthand scope of the present invention should not be limited by any of theabove-described exemplary embodiments.

1. A method of providing a frame for data communication in acommunication system, comprising: generating a frame comprising one ormore subframes, each subframe comprising one or more unit subframes,each unit subframe comprising a fixed length duration T_(u-sub), andgenerating a frame synchronization signal and a frame control signal forcontrolling the subframes in the frame.
 2. The method of claim 1,further comprising generating directionality information for eachsubframe in the frame.
 3. The method of claim of 2, wherein thedirectionality information indicates whether the subframe is used fordownlink transmission or uplink transmission.
 4. The method of claim of3, wherein the directionality information comprises a direction controlbit.
 5. The method of claim 2, wherein the directionality informationindicates whether the subframe is used for downlink transmission, uplinktransmission, or reserved.
 6. The method of claim 2, wherein thedirectionality information indicates whether the channel bandwidthwithin the subframe is used for downlink transmission, uplinktransmission, or reserved.
 7. The method of claim of 2, wherein theframe synchronization signal and the frame control signal are located ina downlink subframe located at the beginning of the frame.
 8. The methodof claim 7, wherein the frame synchronization signal is easilydistinguishable from other signals in the frame, and from framesynchronization signals of other transmission sources using the sametransmission medium.
 9. The method of claim 7, wherein the framesynchronization signal exhibits strong autocorrelation properties andweak cross-correlation properties with other signals in the frame, andwith frame synchronization signals of other transmission sources usingthe same transmission media.
 10. The method of claim of 7, wherein theframe control signal comprises the directionality information, astarting time location, and a time duration T_(sub) for each subframe inthe frame.
 11. The method of claim of 10, wherein the starting timelocation of the subframe in the frame is specified by a time offset fromthe start of the frame.
 12. The method of claim of 11, wherein the timeoffset of the subframe is expressed as an integer number of T_(u-sub).13. The method of claim of 12, wherein the time offset of the subframeis expressed as the sum of the time durations of all the precedingsubframes in the frame.
 14. The method of claim of 10, wherein thedirectionality information, the starting time location, and the timeduration T_(sub) for each subframe in the frame are selected from a setof predefined settings, and are not individually signaled.
 15. Themethod of claim of 14, further comprising transmitting the selected setof predefined settings to a mobile station via the frame control signal.16. The method of claim 2, further comprising: generating one or moreframe partitions in the frame, each frame partition comprising one ormore subframes, and generating a frame partition control signal for eachframe partition comprising for controlling the subframes in the framepartition.
 17. The method of claim of 16, wherein the frame controlsignal comprises the number of frame partitions in the frame.
 18. Themethod of claim of 16, wherein the frame partition control signal islocated in a downlink subframe located at the beginning of the framepartition, and comprises the directionality information, a starting timelocation, and a time duration T_(sub) for each subframe in the framepartition.
 19. The method of claim of 18, wherein the starting timelocation of the subframe in the frame partition is specified by a timeoffset from the start of the frame partition.
 20. The method of claim of19, wherein the time offset of the subframe is expressed as an integernumber of T_(u-sub).
 21. The method of claim of 20, wherein the timeoffset of the subframe is expressed as the sum of the time durations ofthe preceding subframes in the frame partition.
 22. The method of claim19, wherein the time offset is predetermined by the predefined locationsand durations of subframes within the frame and by the location andduration of the frame partition within the frame.
 23. The method ofclaim of 18, wherein the frame partition control signal comprising astarting time location of a succeeding frame partition in the frame. 24.The method of claim of 1, wherein each subframe comprises one or moresubframe partitions, each subframe partition comprises one or more unitsubframes.
 25. The method of claim of 24, wherein the subframe comprisea subframe partition control signal, the subframe partition controlsignal comprise a starting time location and a time duration T_(sub) foreach subframe partition in the subframe.
 26. The method of claim of 24,wherein the frame partition control signal comprise a starting timelocation and a time duration for each subframe partition in thesubframe.
 27. The method of claim 24, wherein units of radio resourcesallocable and individually or collectively identifiable fortransmissions are defined within the total radio resources available fortransmissions within a subframe partition.
 28. The method of claim 24,wherein units of radio resources allocable and individually orcollectively identifiable for transmissions are defined within the totalradio resources available for transmissions within a unit subframe. 29.The method of claim of 1, wherein each unit subframe comprises one ormore OFDM symbols.
 30. The method of claim of 29, wherein the unitsubframe comprises an idle time at the end of the unit subframe.
 31. Themethod of claim of 29, wherein the unit subframe comprises asynchronization signal at the beginning of the unit subframe.
 32. Themethod of claim of 1, wherein T_(u-sub) is equal to 0.5, 0.675, 1, 1.25,1.5, or 2 ms.
 33. The method of claim of 1, wherein the frame comprisesa fixed length duration T_(frame), and T_(frame) is equal to 5, 10, or20 ms.
 34. A method of spectrum sharing between a first communicationsystem and a second communication system, the method comprising:transmitting a first frame by the first communication system, the firstframe comprising one or more subframes, each subframe comprising one ormore unit subframes, each unit subframe comprising a fixed lengthduration T_(u-sub), wherein the first frame comprises directionalityinformation for each subframe that indicates whether the subframe isused for downlink transmission, uplink transmission, or reserved,transmitting a second frame by the second communication system, thesecond frame comprising one or more subframes, wherein the second frameoccupies the time durations of the reserved subframes in the firstframe.
 35. The method of claim 34, wherein the first frame comprises aframe synchronization signal and a frame control signal in a downlinksubframe located at the beginning of the first frame.
 36. The method ofclaim of 35, wherein the frame control signal comprises thedirectionality information, a starting time location, and a timeduration T_(sub) for each subframe in the frame.
 37. The method of claimof 34, wherein the second communication system does not require full useof its operating spectrum at all times.
 38. The method of claim 34,wherein the first communication system and the second communicationsystem have different sub-carrier spacing.
 39. The method of claim 34,wherein the first communication system and the second communicationsystem have different symbol times.
 40. The method of claim 34, whereinthe first communication system and the second communication system havedifferent OFDM/OFDMA cyclic prefix durations.
 41. The method of claim34, wherein the first communication system and the second communicationsystem have different channel bandwidths.
 42. The method of claim 34,wherein the first communication system and the second communicationsystem have different center frequencies.
 43. The method of claim 34,wherein the reserved subframes occur periodically in the first frame,and the first frame comprises a time duration equal to an integermultiple of a minimum periodicity of the reversed subframes.
 44. Themethod of claim 43, wherein the second frame comprises a time durationequal to the minimum periodicity of the reversed subframes.
 45. Themethod of claim 34, wherein the reserved subframes are so situated inthe first frame that the second frame satisfies a timing requirement ofthe second communication system.
 46. The method of claim 34, wherein thefirst communication system has a sub-carrier spacing of 12.5 kHz. 47.The method of claim 46, wherein the first carrier supports three cyclicprefix lengths: 2.5, 10, and 15 μs.
 48. The method of claim 34, whereinthe first communication system has a sub-carrier spacing of 25 kHz. 49.The method of claim 34, wherein the reserved subframes are not used bythe first OFDMA communication system for data transmission.
 50. Themethod of claim 49, wherein the first communication system complies withIEEE 802.16m, and the second communication complies with IEEE 802.16e.51. The method of claim 34, wherein the first communication and thesecond communication operate on the same carrier.
 52. The method ofclaim 34, wherein the first frame comprises a first preamble, the secondframe comprises a second preamble, and the first preamble is orthogonalto the second preamble.
 53. The method of claim 34, wherein the timeduration of the first frame is an integer multiple of the second frame.54. The method of claim 53, wherein the time duration of the secondframe is 5 milliseconds.
 55. The method of claim 34, wherein the firstframe comprises one or more frame partitions, each frame partitioncomprises one or more subframes.
 56. The method of claim of 55, whereineach frame partition comprises a frame partition control signal forcontrolling the subframes in the frame partition, the frame partitioncontrol signal comprises the directionality information, a starting timelocation, and a time duration T_(sub) for each subframe in the frame.57. The method of claim 55, wherein each subframe comprises one or moresubframe partitions, each subframe partition comprises one or more unitsubframes.
 58. The method of claim of 57, wherein each subframecomprises a subframe partition control signal for controlling thesubframe partitions in the subframe, the subframe partition controlsignal comprising a starting time location, and a time duration T_(sub)for each subframe partition in the subframe.
 59. The method of claim of58, wherein the subframe partition control signal comprisesdirectionality information for each subframe partition indicates whetherthe subframe partition is used for downlink transmission, uplinktransmission, or reserved.
 60. The method of claim 59, furthercomprising transmitting the second frame by the second communicationsystem during the time durations of the reserved subframe partitions inthe first frame.
 61. The method of claim 34, wherein the directionalityinformation for each reserved subframe in the first frame furtherindicates whether the channel bandwidth of the reserved subframes isused for downlink transmission, uplink transmission, or reserved, andthe reserved channel bandwidth of reserved subframes is not used by thefirst communication system for transmitting the reserved subframes. 62.The method of claim 61, further comprising the first communicationtransmitting the reserved subframes in the first frame on the channelbandwidth that is not reserved.
 63. The method of claim 62, wherein thefirst communication system is an OFDMA communication system.
 64. Themethod of claim 61, wherein the channel bandwidth of the secondcommunication system does not fully overlap with the channel bandwidthof the first communication system.
 65. The method of claim 64, furthercomprising the second communication transmitting the second frame on thereserved channel bandwidth.
 66. A method of spectrum sharing between afirst communication system and a second communication system, the methodcomprising: transmitting a first frame by the first communicationsystem, the first frame comprising one or more subframes, each subframecomprising one or more unit subframes, each unit subframe comprising afixed length duration T_(u-sub), wherein the first frame comprisesdirectionality information for each subframe that indicates whetherregions of frequency-time resources of the subframe are used fordownlink transmission, uplink transmission, or reserved; transmitting asecond frame by the second communication system, the second framecomprising one or more subframes, wherein the second frame occupies thereserved regions of frequency-time resources of the subframes in thefirst frame.
 67. A method of frame control in a communication system,the method comprising: transmitting a first frame on a first carrier,the first frame comprising one or more frame partitions, each framepartition comprising one or more subframes, each subframe comprising oneor more unit subframes, each unit subframe comprising a fixed lengthduration T_(u-sub), transmitting a second frame on a second carrier, thesecond frame comprising one or more frame partitions, each framepartition comprising one or more subframes, wherein each frame partitionin the first frame has a corresponding frame partition in the secondframe.
 68. The method of claim of 67, wherein the first frame comprisesa frame synchronization signal and a frame control signal in a downlinksubframe located at the beginning of the first frame.
 69. The method ofclaim of 67, wherein each frame partition in the first frame comprises aframe partition control signal for controlling the subframes in theframe partition and in the corresponding frame partition in the secondframe in a downlink subframe located at the beginning of the framepartition.
 70. The method of claim of 69, wherein the frame partitioncontrol signal comprises directionality information, a starting timelocation, and a time duration T_(sub) for each subframe in the framepartition and in the corresponding frame partition in the second frame.71. The method of claim of 70, wherein the directionality informationindicates whether the subframe is used for downlink transmission oruplink transmission.
 72. The method of claim of 70, wherein the framepartition control signal comprising a starting time location of asucceeding frame partition in the first frame, and a correspondingsucceeding frame partition in the second frame.
 73. The method of claim70, wherein the frame partition control signal comprises centerfrequency and bandwidth of the second carrier.
 74. The method of claim70, wherein the frame partition control signal comprises an identifierfor the second carrier.
 75. The method of claim 70, wherein the framepartition control signal comprises information regarding mobile stationassignment on the second carrier.
 76. The method of claim 70, whereinthe frame partition control signal comprises information regardingresources for uplink data transmission on the second carrier.
 77. Themethod of claim 70, wherein the frame partition control signal comprisesinformation regarding resources for downlink data transmission on thesecond carrier.
 78. The method of claim 67, wherein there is a timedelay T_(f,offset) between a frame partition in the first frame and acorresponding frame partition in the second frame.
 79. The method ofclaim 78, wherein T_(f,offset) is configurable based on the secondcarrier.
 80. The method of claim 78, wherein T_(f,offset) allows amobile station to switch to the second carrier to receive or transmitthe corresponding frame partition in the second frame after receivingand processing the frame partition control signal on the first carrier.81. The method of claim 67, wherein a frame partition in the first frameand the corresponding frame partition in the second frame have the sametime duration.
 82. The method of claim 67, wherein a frame partition inthe first frame and the corresponding frame partition in the secondframe have different time durations.
 83. The method of claim 67, whereinthe first carrier has a sub-carrier spacing of 12.5 kHz.
 84. The methodof claim 83, wherein the first carrier supports three cyclic prefixlengths: 2.5, 10, and 15 μs.
 85. The method of claim 67, wherein thefirst carrier has a sub-carrier spacing of 25 kHz.
 86. The method ofclaim of 67, wherein each subframe in a frame partition in the firstframe has a corresponding subframe in the corresponding frame partitionin the second frame, and the starting time location and time durationT_(sub) for each subframe in the first frame are equal to the startingtime location and time duration of the corresponding subframe in thesecond frame.
 87. The method of claim 86, wherein all the subframes inthe first frame are used for downlink transmission, and all thesubframes in the second frames are used for uplink transmission.
 88. Themethod of claim 87, further comprising a base station transmitting asubframe in the first frame and a subframe in the second framessimultaneously.
 89. The method of claim 87, further comprising a mobilestation transmitting a subframe in the first frame and a subframe in thesecond frames simultaneously.
 90. A method of configuring carriers in anOrthogonal Frequency Division Multiplexing (OFDM) or OrthogonalFrequency Division Multiple Access (OFDMA) communication system, themethod comprising: setting up a first carrier with a first centerfrequency and a first channel bandwidth; setting up a second carrierwith a second center frequency and a second channel bandwidth, whereinthe first carrier and the second carrier have a same subcarrier spacing,the first channel bandwidth is adjacent to the second channel bandwidth,the first center frequency and the second center frequency is separatedby an integer number of a frequency step, and the frequency step is aninteger number of the subcarrier spacing.
 91. The method of claim 90,further comprising transmitting signals on subcarriers of the firstcarrier without causing substantial interference to subcarriers in thesecond carrier.
 92. The method of claim 91, wherein the subcarrierspacing is 12.5 kHz.
 93. The method of claim 90, further comprising abase station communicating simultaneously with a first mobile station onthe first carrier and a second mobile station on the second carrier,wherein the first carrier and the second carrier are processed by thebase station as a single aggregated OFDM/OFDMA carrier.
 94. The methodof claim 93, further comprising transmitting signals on subcarriers ofthe aggregated OFDM/OFDMA carrier without causing substantialinterference between subcarriers of the first carrier and subcarriers ofthe second carrier.
 95. The method of claim 93, wherein the subcarrierspacing is 12.5 kHz.